Production of artificial teeth



June 19, 1934. LUTHY 1,963,207

PRODUCTION OF ARTIFICIAL TEETH Filed July 5, 1932 Patented June 19, 1934 UNITED STATES PATENT OFFlCE PRODUCTION OF ARTIFICIAL TEETH Alfred Liithy, Aarau, Switzerland Application July 5, 1932, Serial No. 620,916 In Germany July 9, 1931 6 Claims.

5 ing effect by the cooperating tooth portions as requisite for a correct mastication.

The contacting portions of the artificial teeth hitherto produced are of distinctly superficial dimensions. In analyzing the cinematics of the lower jaw it was found, however, that areal contact between coacting teeth is not consistent with the natural movements performed by the lower jaw. From the point of View of cinematics the lower jaw must be taken as a rigid body which is guided in two points (condyles) by two surfaces (the corresponding articular cavities).

For the following it will be assumed that the small surface elements of the articular cavities over which the condyles are moving correspond- 20 ingly to the small deviations from the central occlusion, as performed by the lower jaw during the masticating operation, can be considered to be small portions of one and the same plane. This plane will be hereinafter called in brief the guide plane. From the cinematics of rigid bodies it is known that any phase of the movement of the body can be considered as the superposition of a translatory movement and a rotatory movement about an instantaneous axis of rotation passing through a certain point. If for illustrating the movements of the jaw the instantaneous axis of rotationis assumed to pass through a common point of the guide plane and the jaw, this point which is fixed on the jaw will be found to travel in the guide plane in different directions during the small movements of, the lower jaw, incidentally to biting forwardly, laterally to the left and right and all intermediary directions. Thus, for providing areal contact between cooperating teeth the rotatory component of the movements of the jaw must either be zero or the instantaneous axis of rotation remain perpendicular to the guide plane. These conditions are, however, as a rule not existing, as during the movement of Y the jaw, incidentally to biting forwardly as well as laterally the rotatory movement takes place about an instantaneous axis of rotation lying in the guide plane. Thus, already for the simplest possible case that the condyles move in a common guide plane the provisions of areal contacting portions is inconsistent with the guide mechanism of the lower jaw, so much more, when it is taken into account that the articular cavities actually form two cylindrical surfaces the axes of which are inclined to each other. If,

therefore, in shaping artificial teeth areal contacting portions are provided, these portions due to the construction of the natural guide mechanism of the lower jaw have the tendency to distort relatively to each other, whereby a detrimental effect is exerted on the abutments, i. e. the alveolar bones, the joints, and the muscles. The reason for this distortion is that the cooperating teeth contact each other peripherally so that the respective pressures are eccentrically' applied thus causing a maximum angular momentum.

Heretofore several forms for artificial teeth have been proposed containing masticating surfaces comprising a plurality of cooperating sockets and cusps. This arrangement subjects the bearing portions to too rigorous straining which causes a premature involution of the alveolar crista. With such an arrangement areal and point contacting portions are alternately provided which, as explained above, is objectionable due to the pressure of the areal portions. The same disadvantage inheres to similar structures which comprise flat or slightly curved sockets.

According to the present invention a pair of cooperating teeth is provided for the three main directions of biting comprising complemental masticating surfaces which during the movements of the lower jaw in these three directions bear against each other by point contact only and are adapted to perform a true rolling motion on each other.

In this manner the invention provides for a satisfactory masticating effect even though the actual masticating action of the cooperating teeth is lessened, each pair of cooperating teeth comprising one active cusp and socket only. With this arrangement the essential requirement for preserving the alveolar crista by reducing the acting forces is fulfilled.

In the accompanying drawing the invention is schematically illustratively exemplified, in which Fig. 1 represents a vertical section on the line II in Fig. 2 of a pair of cooperating teeth having a single point of contact and comprising a convex part in the form of a solid with symmetrical axial sections in all directions and a concave part or socket of a trigonal form,

Fig. 2 is a cross-section on the line 11-11 in Fig. 1,

Fig. 3 is a vertical section similar to Fig. 1 with the axis of the convex part or cusp inclined,

Fig. 4 is a vertical section similar to Fig. l on the ing teeth having two points of contact,

line IVIV in Fig. 5 of a pair of cooperatl a; from the two-point contact Fig. 5 is a cross section on the line V-V in Fi 4,

Fig. 6 is again a vertical section similar to Fig. 1 on the line VI-VI in Fig. 7 for a pair of cooperating teeth having three points of contact,

Fig. '7 is a cross section on the line VII-VII in Fig. 6, i

Fig. 8 represents a vertical section on the line VIII-VIII in Fig. 9 of a pair of cooperating teeth having one point of contact and comprising a trigonal cusp and a concave part in the form of a socket with symmetrical axial sections in all directions,

Fig. 9 is a cross section on Fig. 8,

Fig. 10 is a vertical section similar to Fig. 8- on the line X-X in Fig. 11 of a pair of cooperating teeth having two points of contact,

Fig. 11 is a cross section on the line XIXI in- Fig. 10.,

Fig. 12 is a vertical section similar to Fig. 8 on the line XIIXII in Fig. 13 of a pair of cooperating teeth having three points of contact,

Fig, 13 is a cross section on the line XIII -XIII in Fig. 12, and

Fig. 14; is. avertical section on a larger scale of a pair of cooperating teeth, similar to those shown in Fig. l, with the center line of pressure acting between the teeth drawn, in.

For a clear understanding of the diiierent modes of contacting, as one, two-, and three-point contact, which arise between two artificial cooperating teeth,. according to the present invention, during the masticating, movements of the lower jaw,

the line IX-IX in M the. following explanation starts from a lateral occlusion, i. e. an intermediate position of this. jaw between the. foremost. position and either extreme lateral position during the biting.

Under this assumption the convex part a or cuspinzthe form of a solid with symmetrical axial sections in all directions,.of the cooperating upper and lower teeth A and B contacts the concave part b or socket, of a trigona1 form,.of the tooth B. in a single point Hone-point contact, (Figs. I and 2) the curvature of the cusp at this point being greater than the corresponding curvature of the socket. Now, supposing that the lower jaw does not move from. this point directly towards the central occlusion, but rather in the, manner of. biting rotationally, the point until the cusp a enters into one of the three corner grooves 2 of the socket b, thereby contacting the socket in two points of contact. 3 for example, as shown in, Fig. 5. On the continuation of the rotational biting movement the cusp a would again move out of the corner groove 2', so that instead of two-point contact again one-point contact would take place. If, however, during this second phase of" movement the lower jaw travels position in the groove 2 towards the central occlusion the cusp rides downwardlyin this corner groove, whereby the grooveserves as aguideforthe cusp. During this downward motionthe cusp is guided by both side walls of the groove. Thus the two-point contact isat all times maintained until the central occlusion is reached inwhich the movement is stoppedby the cusp contacting the socket in a third point 4 as: shown in Fig. 7. The-manner in which the second phase of movement is carried out is evident from the Figs. 4 and 6. In the latter the point: 4 which lies: in the central vertical plane is also visible the same as point I of Fig; 2'is visible in Fig. l.

In all threepositi'onsx of the; cusp: the sonof contact travels tacting between the same and the socket occurs during the described movement in the manner of point contacting, in contradistinction to areal contacting, as the curvature of the walls of the socket is always smaller at the places of contact than that of the cusp. Thus, during the movements of the jaw alternately one-, twoor threepoint contact is provided between the cooperat ing tooth portions so that in shaping the artificial teeth it is not necessary to make provision for the axis of the cusp to assume a certain disposition relatively to the prosthetic plane. It is immaterial whether the axis of the cusp extends perpendicularly to this plane or in an inclined position thereto, as point contact is in all cases assured during the relative movements of the teeth (Fig. 3). The cooperating tooth portions are free to perform a rolling motion relatively to each other without the position of the center line of the acting pressure between the teeth materially changing. This will be clearly seen in Fig. 14 which shows the two cooperatingteeth A, B on a larger scale with the center line 0- of the pressure acting between the teeth drawn in. On the occurrence of a rolling motion the point, of contact shifts to a position adjacent to this point, whereas the direction of the center line remains the same as compared with areal contact where on the occurrence of the slightest relative distortion between cooperating teeth the center line of pressure shifts to the periphery of the contacting surfaces. Moreover, when areal contacting portions are provided the direction of the axis of the cusp is necessarily fixed.

The description referring to the Figs. I Y of the drawing may also serve f operation of the teeth shown in the Figs. 8 -13 when it is borne in mind that in the latter series of figures the cusp a" of the tooth A is trigonal-shaped, whereas the concave part b of the tooth B is in the form of a socket with symmetrical axial sections in all directions and constituted by circular circumferential portions. In the Figs. 8-13 the rounded-off corners of thetrigonalcusp w are designated by 2 and the points corresponding to the points 1, 3 and- 4 of the Figs. 1-7 by 1, 3 and 4. Also here one-, twoor three-point contact is provided between the cooperating tooth portions respectively. In all positions of engagement point contact is assured between the tooth portions by the curvature of the edges of the cusp being greater than that of the bottom of the socket. Thus the teeth are again free to effect a true rolling motion relatively to each other.

Various modifications may be made by those skilled in the art without departing from the invention as defined in the following claims. I claim, I

I. In a denture for the upper and lower jaw the combination of pairs of coacting artificial teeth, a convex occlusal surface on one toothof' each pair and a correlated concave occlusal' surface on the other tooth of the same pair, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between enacting teethand a true rolling motion of the occlusal surfaces of said teeth on each. other during the movements of the lower jaw for biting in the three. main directions.

2. In a denture for the; upper and lower jaw the combination. of pairs of coacting. artificial teeth, a convex occlusal surface on. the. upper or explaining the tooth of each pair and a correlated occlusal surface in the form of a socket having a trigonalshaped interior wall on the. lower toothof the same pair, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between coacting teeth and a true rolling motion of the occlusal surfaces of said teeth on each other during the movements of the lower jaw for biting in the three main directions.

3. In a denture for the upper and lower jaw the combination of pairs of coacting artificial teeth, an occlusal surface in the form of a trigonal-shaped cusp with rounded corners on the upper tooth and a correlated concave occlusal surface on the lower tooth of the same pair, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between coacting teeth and a true rolling motion of the occlusal surfaces of said teeth on each other during the movements of the lower jaw for biting in the three main directions.

4. In a denture for the upper and lower jaw the combination of pairs of coacting artificial teeth, a convex occlusal surface on the upper tooth and a correlated occlusal surface in the form of a socket having a trigonal-shaped interior wall on the lower tooth of at least one pair, an occlusal surface in the form of a trigonalshaped cusp with rounded corners on the upper tooth and a correlated concave occlusal surface on the lower tooth of at least one other pair, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between coacting teeth and a true rolling motion of the occlusal surfaces of said teeth on each other during the movements of the lower jaw for biting in the three main directions.

5. A pair of coacting artificial teeth for the upper and lower jaw having a convex occlusal surface of a substantially circular circumferential contour on the upper tooth, and a correlated occlusal surface in the form of a socket having a trigonal-shaped interior wall on the lower tooth, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between coacting teeth and a true rolling motion of the occlusal surfaces of said teeth on each other during the movements of the lower jaw for biting in the three main directions.

6. A pair of coacting artificial teeth for the upper and lower jaw having an occlusal surface in the form of a trigonal-shaped cusp with rounded corners on the upper tooth and a correlated concave occlusal surface of a substantially circular circumferential contour on the lower tooth, and cooperating masticating portions of different curvatures provided on said respective occlusal surfaces of the coacting teeth for the three main directions of biting, thereby ensuring point contact between coacting teeth and a true rolling motion of the occusal surfaces of said teeth on each other during the movements of the lower jaw for biting in the three main directions.

ALFRED L'UTHY. 

